The “franking” privilege lets lawmakers send mail to constituents with their signatures in the place of postage stamps, though the cost to send the mailings is paid for later out of their office budgets.

Duckworth, a freshman Democrat from Hoffman Estates, said a bill she introduced Tuesday will require lawmakers to pay for postage in advance. But it would not reduce the amount of money lawmakers may spend on mail to constituents, said Duckworth’s spokesman, Anton Becker

“As members of Congress, we lead by example,” she said in a statement. “With so many working families out there trying to make ends meet, it’s important that we meet the same obligations that our neighbors meet. Removing the franking privilege for Congress is a small step we can take to show the American people we are here to work for them.”

The bill’s co-sponsor is U.S. Rep. Rob Woodall of Georgia. It has the backing of the two watchdog groups, the National Taxpayers Union and Public Citizen.

Duckworth is running for re-election Nov. 4 against Republican Larry Kaifesh of Carpentersville. He could not immediately be reached for comment today.

The “franking” privilege dates to the Continental Congress in 1775 and is used to send millions of dollars worth of mail through the U.S. Postal Service without requiring lawmakers to pay for the postage in advance, Duckworth and Woodall said.

Reforms in the last 25 years have reduced franking expenditures, a Congressional Research Service report has said. Still, in the 435-seat House, the tab for mass mailings over a 12-year period ending in 2008 reached $224.5 million, for an annual average of $18.7 million.

A story in 2011 by the Chicago Tribune detailing franked mail sent by Illinois’ House lawmakers found one member sent mailings to bestow a “special congressional recognition” on high school graduates. Others sent constituents glossy wall calendars showcasing Washington’s top tourist sites.

Rules govern the type of congressional mailings that may be “franked.” Still, the newspaper found the bill for franked mail for House members from Illinois was $4.27 million over a 30-month period ending in June 2011.